PHY.4:2 - Problem

A formula can be easy to calculate with while admitting a physically impossible direction, an unjustified dependence or an omitted influence. Choosing the formula first can hide those differences.

Conversely, an appeal to symmetry or conservation can appear to determine a law while leaving important functions or parameters free. The task is to obtain the restriction that follows from the physical comparison and carry its remaining freedom into the next construction or inquiry.